The existing iterator for_each_compatible_node() searches for each
compatible node starting from the root of the loaded device tree.
This means it only works on the barebox device tree and not the tree
to be passed to the Linux kernel, which is what an of_fixup would
probably want to use.

This adds for_each_compatible_node_from(), which takes an additional
parameter of a root to search from.  This could be the device tree to
be used for the kernel.  It could also be used to search just a
subtree.

Signed-off-by: Trent Piepho <tpiepho@kymetacorp.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>